Effects of Pb and carbonate substitutions on the superconducting properties of TlSr4Cu2OzCrO4

Abstract

We have investigated the effects of Pb and carbonate substitutions on the phase formation and the superconducting properties of the intergrowth superconductor TlSr4Cu2OzCrO4. X-ray diffraction data showed that nearly single-phase samples with tetragonal structure were obtained in the compositions (Tl1-xPbx)Sr4Cu2OzCrO4 (0 ≤ x ≤ 0.5) and (Tl0.5Pb0.5)Sr4Cu2Oz(CrO4)1-y(CO3)y (0 ≤ y ≤ 1.0). Resistivity measurements indicated that the transition temperature decreased significantly as the Pb doping content x increased to x = 0.5. In contrast to the Pb doping effects, the carbonate substitution in the (Tl0.5Pb0.5)Sr4Cu2Oz(CrO4)1-y(CO3)y system resulted in an improvement of the superconducting transition temperature up to y = 0.9. The y = 1.0 sample showed a reduced transition temperature, compared to the x = 0.9 sample. The experimental results are discussed in conjunction with the change in hole carrier concentration due to the Pb and carbonate substitutions, based on the data from room temperature thermoelectric power measurements.